Bellows pipe construction

ABSTRACT

A bellows pipe construction and method for manufacturing are disclosed wherein helically wound coils of longitudinally corrugated strip are joined with an interlocking seam. Thereafter, the interlocking seam is deformed to position the edges of the strip in substantial parallelism with the axis of the pipe. The resulting pipe can be extended or shortened for installation and will further adjust and accommodate ground movement without substantial loss of strength.

This application is a division of application Ser. No. 639,123, filedJan. 9, 1991 now U.S. Pat. No. 5,074,138.

SUMMARY OF THE INVENTION

This invention relates generally to the manufacture and construction ofa bellows pipe made from metallic strip material for use as undergroundconduit. A bellows type construction allows axial expansion andcontraction and may be laid along a tortuous ditch or pathway. Such pipealso is capable of accommodating ground movements as occur duringearthquakes, which result in bending and axial expansion andcontraction. Although bellows pipe constructions are known in the art,there are no known underground applications of such pipe made fromhelically formed and seamed metallic strip material. The primary problemwhich may be encountered in using such pipe is that the helical stripfrom which the pipe is made may be become unseamed as a result ofrepeated or excessive axial expansions and contractions.

In brief, the invention described herein provides a novel constructionfor forming a bellows pipe with metallic strip material wherein afterseaming the strip at an angle of approximately 20° or greater relativeto the pipe's axis the seam is then deformed to position the seam andthe interlocking edges of the strip parallel to the pipe axis. Theresulting pipe construction exhibits substantially greater strengthcharacteristics and resistance to unseaming than previously knownhelically formed and seamed pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings forming a part of this application:

FIG. 1 is a perspective view of a preferred embodiment of the inventionin a bellows pipe made from metallic strip material;

FIG. 2 is an enlarged longitudinal section taken through one wall andseam of the pipe as initially formed;

FIG. 3 is a longitudinal section taken through the same wall and seamafter deforming the seam to position it and the edges of strip in aneutral plain substantially parallel to the axis of the pipe; and

FIG. 4 is a longitudinal section through one wall and seam at a pipethat is deformed inwardly to a position in line with the innermostcorrugated surfaces.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiment of the invention shown in FIG. 1 illustrates abellows type pipe from metallic strip. In the conventional manner planaror flat strip is longitudinally corrugated to form a strip having asubstantially sinusoidal cross section defined by alternating ridges 10and grooves 11. Ridges 10 extend from grooves 11 and cross the neutralplane of the strip (indicated by broken line 12) at an angle φpreferable greater than 60°. This provides sufficient material in thestrip and resulting pipe to permit both expansion and contraction afterthe pipe is formed.

In the preferred embodiment the pipe utilizes a conventionalinterlocking seam 13 as shown in U.S. Pat. No. 3,246,692. Accordingly,prior to coiling the strip material the edges are prepared or formed forproducing an interlocking seam. Thereafter, the strip material ishelically coiled and the opposite edges of the coiled strip are engagedin an interlocking seam, as shown in FIG. 2. This results in a bellowspipe construction which, although satisfactory for many purposes, doesnot possess sufficient strength in the seam to withstand severe andrepeated axial expansions and contractions. It has been found, however,that by deforming the interlocking seam and positioning the edges insubstantial parallelism with the axis of the pipe increased strength isobtained to resist unseaming. Two such pipe structures are shown inFIGS. 3 and 4.

The initial step of interlocking the edges, as shown in FIG. 2, ispreferable carried out by engaging the edges radially intermediate theexterior surfaces of the ridges and grooves at an angle Θ ofapproximately 20° or greater relative to the axis of the pipe. If formedat a lesser angle, difficulty will be experienced in engaging the edgesusing conventional roller dies.

A preferred method of manufacture employs a process where the pipecorrugations are formed with a helix angle of 75° or greater relative tothe pipe axis. This allows for exceptional expansion and contraction ofthe pipe. Also, a preferred corrugation of the strip is one that issubstantially sinusoidal in cross section as defined by the alternatingridges 10 and grooves 11. As shown in FIGS. 2 and 3 the ridges extendfrom grooves 11 and cross the neutral plain 12 of the strip at an anglegreater than 60°. This contributes to the structural characteristics ofthe pipe and its ability to expand and contract from the "asmanufactured" condition.

As shown in FIG. 3, the interlocking seam is deformed to a radialposition relative to the pipe axis such that the strip edges aremaintained radially intermediate the exterior surfaces of the ridges andgrooves. This is a preferred construction where strength is of paramountimportance. However, for some applications it may be desirable to deformthe seam to a position that is the same radial distance from the pipeaxis as are grooves 11, as shown in FIG. 4. This construction provides amore uniform flow surface within the pipe to reduce turbulence acrossthe lock seam. This will be of substantial importance where used incombination with a cylindrical liner having substantially the sameinternal diameter as the lock seam.

The spacing of corrugations as well as their size and depth areimportant to the overall strength of the pipe and its ability to expandand contract. Quality pipe constructions have been formed with a modulusor constant spacing between ridges and grooves of approximately 1/2 inchand a depth spacing of between 1/4 inch and 1/2 inch. The preferred sizeof corrugations is one that is semicircular and formed with a radius ofcurvature less than 1/4 inch.

Although preferred embodiments of the invention have been illustratedand described, various modifications and changes may be resorted towithout departing from the spirit of the invention or the scope of theappended claims, and each of such modifications and changes iscontemplated.

What is claimed is:
 1. A bellows pipe construction for use inunderground installations, comprising helically wound coils ofcorrugated strip formed on a pipe axis and having a helix angle ofgreater than 75° relative to the pipe axis, said corrugated strip beinginitially formed with ridges and grooves that are symmetrical andsubstantially arcuate, and formed to opposite sides of a neutral planeintermediate the ridges and grooves, adjacent ridges and groovesextending on a tangent plane that crosses the neutral plane of thecorrugated strip at an angle greater than 60°, whereby the length of themanufactured pipe can be extended or shortened for installation and willfurther adjust and accommodate ground movement without substantial lossof strength, said helically wound coils of strip being edge connectedwith a continuous seam at an angle of approximately 20° or greaterrelative to the axis of the pipe, said seam being then deformed toposition, the edges of the strip in substantial parallelism with theaxis of the pipe.
 2. The bellows pipe construction of claim 1, saidridges and grooves being formed on a modulus spacing of approximately1/2 inch.
 3. The bellows pipe construction of claim 1, the depth of thecorrugated strip from a ridge surface to a groove surface beingapproximately 1/4 inch to 1/2 inch.
 4. The bellows pipe construction ofclaim 1, said corrugated strip being formed with semi-circular ridgesurfaces and groove surfaces, the radius of curvature being less than1/4 inch.